Water heater

ABSTRACT

A water heater or boiler, comprising a conduit ( 2 ) having an inlet ( 10 ) and an outlet ( 20 ), means for causing water to flow h said conduit ( 2 ) from said inlet ( 10 ) to said outlet ( 20 ), and one or more radio frequency wave heating sources ( 3 ) arranged such that water is heated thereby as it flows through said conduit ( 2 ) from said inlet ( 10 ) to said outlet ( 20 ). The radio frequence wave heating source ( 3 ) is preferably a microwave heating source, and the apparatus may include one or more waveguides ( 7 ) for directing the microwaves towards the conduit ( 2 ). The invention provides a water heater or boiler which can heat water on demand (but required the need for a storage tank or the like) using microwave or other radio frequency heating source. One or more microwave radiation absorption members (not shown), such as a metal rod or piece of wire wool, may be disposed in the water to be heated to significantly increase the efficiency of the heater.

This invention relates to a water heater and, more particularly, to ahighly efficient, relatively safe, relatively low maintenance waterheater for use in both commercial, domestic and industrial environments.

Electric water heating devices or boilers are well known. Such devicesgenerally comprise a water tank for holding a predetermined volume ofcold water for heating, and the water tank is conventionally lagged orsurrounded by a thermally insulating outer casing. Within the tank isprovided an electric resistance or element which becomes hot whenelectrical current is passed therethrough and heats the water within thetank to a predetermined desired temperature.

Such electric water heating devices are conventionally used inenvironments where space and ventilation are minimal because they aregenerally considered to be relatively safe in operation. However, thereare a number of disadvantages associated with this type of water heater,as follows. Firstly, electricity is a relatively expensive power source;and secondly, the electric element quickly becomes covered withlimescale which greatly reduces its heating efficiency, which drawbackcan only be alleviated by frequent maintenance operations to clean orreplace the element. As a result of both of these issues, the operationand maintenance costs of an electric water heater or boiler arecomparatively high.

In environments where space is not necessarily limited, and wheresufficient ventilation can be readily provided, it is more common toemploy gas water heaters or boilers, largely because gas is a relativelylow-cost power source in comparison to electricity. Again, many suchdevices generally comprise a large water tank for holding apredetermined amount of water to be heated, the tank being surrounded bysome form of thermally insulating material, as in the case of anelectric water heater or boiler. However, another type of gas boiler,namely the combination boiler, exists which heats water on demand anddoes not require a water tank as such. Although such devices are smallerthan the traditional water tank arrangements, they are still relativelylarge and cumbersome making them unsuitable for some smallerenvironments.

Although gas water heaters tend to be much cheaper to operate than theirelectric equivalents, they still have a number of disadvantagesassociated with them. Firstly, the installation of a gas water heater orboiler requires adherence to very stringent ventilation and other safetyregulations. In particular, the device must be provided within anenvironment which is suitably ventilated to prevent the build up ofdangerous combustion products resulting from the burning of gas.Secondly, this type of water heater or boiler, especially thecombination type gas boiler, still suffers from the problems associatedwith a large build up of limescale which greatly reduces its heatingefficiency and can only be overcome by regular maintenance andreplacement of components.

European Patent Application No. 0849546 describes a water heatercomprising a water tank for holding a predetermined volume of water tobe heated and a microwave heating source for heating the water in thetank. One of the main advantages of employing a microwave heating sourcefor this purpose is the substantial reduction in the build up of mineraldeposits within the equipment, thereby substantially reducing themaintenance costs thereof. As such, the water heating equipmentdescribed in the above-mentioned document is intended to provide a waterheating capability which is relatively efficient and remains so overlong periods of time.

However, the arrangement described in European Patent Application No.0849546 still suffers from the drawback that the equipment is relativelylarge and cumbersome and, as such, can only be installed in anenvironment where a sufficiently large area is available. Further, ittakes a relatively long period of time to heat a whole tank full ofwater to the required temperature and, as such, is unsuitable for use ina situation where hot water is required substantially immediately.

U.S. Pat No. 4,152,567 describes water heating apparatus comprising aresonant cavity having a magnetron (or microwave energy source) coupledthereto. The resonant cavity has an inlet for allowing cold water toflow into the resonant cavity for heating by the microwave energysource, and an outlet for allowing the heated water to flow back out ofthe resonant cavity for use as required. Grid wires are provided acrossthe inlet and outlet to prevent radiation from propagating down thewater pipe leading into the inlet and the outlet and, as such, haveopenings therein less than a half-wave length of the radiant energy atthe operating frequency of the magnetron. The grid wire structure isintended to provide electrical continuity within the heating cavity andachieves microwave shielding while allowing water to flow through theheating system without fluid flow impairment.

However, this system suffers from a number of drawbacks. Firstly, if thewater is permitted to flow through the resonant cavity at the same rateas it is fed from a standard water supply, it is unlikely to be heatedto a sufficient temperature while it is in the resonant cavity to makeit suitable for use in many commercial and domestic applications.Secondly, the requirement for the grid wire structure renders theoverall system unnecessarily complex, expensive and susceptible tofailure.

We have now devised an arrangement which overcomes all of the problemsoutlined above.

Thus, in accordance with the first aspect of the present invention,there is provided fluid heating apparatus comprising a heating cavityand at least one substantially fluid-tight pipe or channel within saidheating cavity, the pipe or channel having an inlet and an outlet, meansfor causing fluid to flow or pass through said pipe or channel from saidinlet to said outlet, and one or more radio frequency wave heatingsources arranged to emit electromagnetic radiation into said heatingcavity such that fluid is heated thereby as it flows through said pipeor channel from said inlet to said outlet.

Also in accordance with the first aspect of the present invention, thereis provided a method of heating fluid comprising the steps of providinga heating cavity and a substantially fluid-tight pipe or channel withinsaid heating cavity, the pipe or channel having an inlet and an outlet,causing fluid to flow through said pipe or channel from said inlet tosaid outlet, applying radio frequency wave radiation into said heatingcavity around said pipe or channel such that fluid is heated thereby asit flows through said pipe or channel from said inlet to said outlet.

The fluid is preferably a liquid, for example water or a water-basedliquid.

Thus, since the fluid flowing or passing through the pipe or channel isisolated from the electromagnetic radiation heating source, noadditional microwave shielding is required in the pipe or channel (orconduit) or at the inlet or outlet thereof. Further, the diameter of theconduit at the inlet and outlet is sufficiently narrow to preventradiation leakage therethrough, thereby eliminating the need for a gridwire structure or similar leakage prevent means at the inlet and outlet.

The term ‘radio frequency’ is well understood in the. art to mean anyfrequency of electromagnetic radiation in the range between 3 kHz and300 gigahertz inclusive. However, the preferred heating source in thiscase is radio frequency in the range 100 MH_(z) to 100 GH_(z), morepreferably 100 MH_(z) to 10 GH_(z), and more preferably around 300MH_(z) to 3 GH_(z), for example, a microwave heating source.

Thus, the first aspect of the present invention provides a fluid (e.g.water) heater which is small, efficient, safe and low maintenance whichpreferably uses microwave energy as the heat source and heats fluid asit flows through a relatively small conduit such that water or otherfluid can be heated on demand, which eliminates, the example, the needfor a large storage tank to hold a volume of water to be heated. Inother words, the heater of the present invention is operable for thecase where large or small fluid volumes are required to be heated, andwill provide fluid or heating facilities on demand if required with nohot fluid storage requirements.

The heater of the first aspect of the present invention is suitable foruse in both domestic and commercial environments, and is sufficientlyflexible to be able to provide hot fluid, such as water to a completebuilding or environment, or just selected areas thereof according torequirements. In other words, the apparatus of the present invention canbe in-line, providing heat or hot water to one heat unit or water tap,or it can be used as a central feeder for more than one heat unit orwater tap. In any event, the apparatus of the present invention iscapable of providing heating or hot water, or other fluid on demand,thereby eliminating the need for any pre-heating of fluid housed in astorage tank.

One exemplary embodiment of the first aspect of the present inventionmay comprise a portable water heater, which may be powered by, forexample, battery or solar power, and which can supply hot water in anenvironment where no other means to heat an existing water supply isavailable and/or where an independent water container exists oraccompanies the present invention in accordance with one exemplaryembodiment thereof.

The apparatus according to the first aspect of the invention may bearranged to heat fluid to a variety of different (selectable)temperatures, possibly in a range between around 20° C. to around 500°C. or more, such that the apparatus could be used to sterilise water ifrequired. Such sterilisation apparatus may be provided in conjunctionwith a water storage tank if necessary (i.e. water sterilised in transitthrough the conduit included in the present invention could betransported to and stored within an airtight storage container forfuture use as required).

Once the required fluid temperature is selected (either by a user or bythe system designer) heating of the fluid flowing through or passing thesystem is preferably controlled by a control unit which may be arrangedto control the rate of flow of fluid into and therefore through theheating area (thereby controlling the period of time for which the fluidis in the heating area being heated). However, in a preferredembodiment, control means are provided for controlling at least thefrequency of the radio frequency source (and optionally also the flow offluid into the system) according to the fluid temperature required to beattained.

In any event, in the case of a possible variable flow rate of fluid intothe system, sensors are preferably provided to detect such flow rateand/or outlet temperature. The output(s) of such sensor(s) arepreferably fed to the control means to control flow rate and/orfrequency of the RF source so as to obtain a substantially constantfluid temperature at the outlet.

frequency of the RF heating source, in the case of a water heater, islikely to be that which makes the skin depth in a domestic/commercialwater supply the same order of magnitude as the conduit diameter. Thiscan be easily calculated by a person skilled in the art, but may beclose to a magnetron frequency of around 1 GH_(z) or more.

The conduit may comprise a helical or otherwise shaped tube or channel,or network of channels or tubes, of any suitable, thermally conductivematerial, for permitting fluid flow therethrough. Alternatively, or inaddition, the conduit may comprise one or more chambers.

One or more waveguides may be provided to aid in the efficienttransmission and direction of the radio frequency waves emitted by theheating source towards the conduit through which the fluid to be heatedis flowing or passing. In a preferred embodiment, it is the commencementof flow of fluid through the conduit (caused, for example, by theturning on of the or a tap connected to the heater or by the switchingon of a or the heating unit connected to the heater) which triggers theoperation of the radio frequency wave heating source. The heating cavitymay comprise or include a single mode waveguide (having a single heatinglocation) and/or a multiple mode waveguide (having a plurality ofheating locations). In either case, means may be provided for slowing ordelaying the flow of fluid through the heating cavity at the, or one ormore of the heating locations. Alternatively, or in addition, means maybe provided for stopping and holding a body of fluid at the, or one ormore of the heating locations, such that a fixed body of fluid isheated.

The apparatus preferably includes cooling means for drawing cooling gasacross the heating source to cool said source. In a preferredembodiment, the gas (once warmed by the passing thereof across theheating source) may be directed towards the conduit through which wateris flowing in order to aid in the heating thereof. Alternatively, or inaddition, the apparatus may include outlet means for venting said warmedgas. The conduit may be wrapped around or otherwise disposed adjacent tothe heating source, so that heat generated thereby is directlytransferred via the conduit to the fluid therein, although additionalcooling means may also be provided.

The apparatus preferably includes a chamber or similar housing in whichelectronic control means, such as temperature control, timer and safetyelectronics may be housed, as required. The apparatus may furthercomprise a removable panel which allows access to one or more componentsof said apparatus, removal of said panel being beneficially arranged torender said apparatus inoperable until said panel is replaced. One ormore of the elements of the heater, particularly the conduit and heatingsource (and waveguide(s) if applicable), are preferably housed within acasing of electrically conductive material which is intended to preventinterference from unwanted electrical disturbances, more preferably aFaraday cage which is an earthed wire or metal screen completelysurrounding the apparatus such that no electric field can be producedwithin the housing by external electric charges and no radio frequencywaves can leak therefrom.

In accordance with the second aspect of the present invention, there isprovided heating apparatus for emitting heat into the surroundingatmosphere, said apparatus comprising a thermally conductive housingcontaining a body fluid therein, when in use, and one or more radiofrequency heating sources for heating said body of fluid in saidhousing, heat from said body of fluid being conducted to said housingand from said housing into the surrounding atmosphere.

The fluid is preferably a fluid, most preferably, water or a water-basedfluid.

An addition to the present invention provides a means of heating, by RF,a radiator containing fluid designed in such a way as to act as a RFchamber. The one or more radio frequency heating sources wouldpreferably be an integral part of the heating apparatus or “radiator”.The apparatus might, beneficially include means for cooling said one ormore RF heat sources and/or means for venting war air, and/or means fortransferring the RF waves into the fluid chamber defined by the internalconfines of the housing, causing the fluid to heat. A small pump may beadded (but not necessarily) to agitate the heated fluid within theradiator or cause it to circulate therein, preferably through awaveguide supporting a radio frequency heating source.

The RF heat source(s) could be mains, generator and/or battery poweredallowing use in domestic and commercial environments or where mainselectricity is not available such as portable buildings or remotebuildings.

This aspect of the invention would allow the installation of a singleunit or a multiple of units whereby the unit or units could beintelligently controlled by a central control unit or locally on eachindividual unit or both. The central control method would preferably bewireless so as to eliminate the need for hard wiring.

Such a radiator could be drained for transit from a drainage plugsuitably positioned, and refilled via a fill plug.

The heating apparatus of the second aspect of the invention essentiallyeliminates the need for plumbing equipment and a central heating systemas traditionally used for gas heating. This significantly reduces thematerials required to develop a domestic or commercial heating system,and by using RF technology the heating process would be highly efficientand significantly less costly. Maintenance costs would also besignificantly reduced and threat of system breakdown causing floodingwould be reduced.

No exhaust gases are generated, so no vent system is required as is thecase with gas central heating systems.

Another benefit of the second aspect of the invention is the eliminationof scale build up enhancing system efficiency.

The described radiator can be moved at any time and relocated in anotherpart of the room or building without the need for plumbing. It can becontrolled so that any number of radiators could be operated at any ordifferent times via control unit that allow complete flexibility.

The radiator design can be flexible and variable to suit any number ofapplications or styles or it could be standard. In each case, the designensures optimum heating efficiency.

The second aspect of the invention can be extended to use in autovehicles where the heating apparatus, designed accordingly, can be usedto preheat the vehicle cabin prior to occupation and independent of thevehicle engine. Additionally, such RF heating apparatus can beincorporated into the engine cooling system allowing the preheating ofthe cooling water so as to assist and make more efficient enginestart-up. In both these cases, the RF heat source can be activatedremotely or locally by timer.

In accordance with a third aspect of the present invention, there isprovided fluid heating apparatus comprising a heating cavity and one ormore radio frequency wave heating sources arranged to emitelectromagnetic radiation into said heating cavity such that a body offluid disposed therein or fluid flowing therethrough is heated, theapparatus further comprising one or more aerials disposed within thebody or flow of fluid to be heated, the or each aeriel comprising amember arranged to transmit or receive electromagnetic waves.

Also in accordance with the third aspect of the present invention, thereis provided a method of heating fluid, comprising the steps of providinga heating cavity within which is disposed a body of fluid to be heatedor through which fluid to be heated is caused to flow or pass, emittingradio frequency wave radiation into said heating cavity such that saidfluid is heated thereby, and providing one or more aerials within saidbody or flow fluid, the or each aerial comprising a member arranged totransmit or receive electromagnetic waves.

The fluid is preferably a liquid, such as water or a water-based liquid.

Once again, the radio frequency wave radiation is preferably microwaveradiation, and the fluid is preferably water.

The provision of one or more aerials within the body or flow of fluid tobe heated significantly increases the efficiency of the heating process.In one specific embodiment, the aerial(s) may comprise at leastpartially, preferably solid, metal member(s) such as one or more metalrods, tubes, pipes, wires or metal pieces or filings. Alternatively, orin addition, the aerial(s) may at least partially comprise a member madeof carbon, or other suitable non-metallic material.

The effect of providing one or more aerials is to concentrate the radiofrequency energy within the body/flow of fluid by reception (and/ortransmission) of the radio frequency energy. This increases the speed atwhich the temperature of the fluid rises and increases the amount ofenergy produced by the radio frequency source that is actually absorbedby the fluid, thereby increasing the efficiency of radio frequencyheating.

The provision of one or more aerials within the systems of the first andsecond aspects of the invention would enhance the performance of suchsystems, but this innovation may have many other applications.

Embodiments of the present invention will now be described by way ofexamples only and with reference to the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional view of a water heater accordingto a first exemplary embodiment of the first aspect of the presentinvention;

FIG. 2 is a schematic cross-sectional view of a water heater accordingto a second exemplary embodiment of the first aspect of the presentinvention;

FIG. 3 is a schematic cross-sectional view of a water heater accordingto a third exemplary embodiment of the first aspect of the presentinvention;

FIG. 4 is a side view of heating apparatus according to an exemplaryembodiment of the second aspect of the present invention;

FIG. 5 is a schematic partial side cross-sectional view of the apparatusof FIG. 4;

FIG. 6A is a partial perspective view of the apparatus of FIG. 4; and

FIG. 6B is a partial perspective view of an alternative exemplaryembodiment of the second aspect of the present invention.

FIG. 7 is a schematic cross-sectional side view of heating apparatusaccording to an exemplary embodiment of the third aspect of the presentinvention;

FIG. 8 is a schematic perspective plan view of heating apparatusaccording to an exemplary embodiment of the present invention;

FIG. 9 is a schematic perspective bottom view of the apparatus of FIG.8; and

FIG. 10 is a schematic perspective view of the apparatus of FIG. 8,illustrating its component parts.

Referring to FIG. 1 of the drawings, a water heater according to a firstexemplary embodiment of the first aspect of the present inventioncomprises a housing 2 of, for example, metal or shielded polymermaterial. Housed within the housing 2 is a helical pipe or channel 1having an inlet 10 and an outlet 20. Also housed within the housing 2 isa microwave radiation source in the form of a magnetron 3 which is acrossed-field microwave tube that produces radio frequency oscillationsin the microwave region. The magnetron 3 may be powered from the mainselectricity supply within the environment in which the water heater isinstalled. Alternatively, or in addition, it may be battery-poweredand/or solar-powered, according to requirements and availability ofcomponents.

A cooling fan 4 is provided in close proximity to the magnetron 3 so asto prevent the magnetron from overheating during prolonged operation.The housing 2 is provided with an air inlet 5 and an air outlet 6, andthe cooling fan 4 operates to draw cooling air from outside the housing2 into the housing 2 through the air inlet 5, across the magnetron 3 andthen expel the warmed air from inside the housing 2 through the airoutlet 6.

The housing 2 is further provided with a separate chamber 8 for housingthe necessary electronic components (not shown) required for controllingthe water heater.

In use, power is supplied to the magnetron 3 which operates to producemicrowave radiation and emit said radiation within the housing 2. Themicrowave radiation generated by the magnetron 3 acts to heat waterwhich is flowing through the helical channel 1 between the inlet 10 andthe outlet 20. Thus, the water is heated as it flows through the channel1 and no storage tank is required: the water can simply be pumped towherever it is required for use directly from the water heater.

Referring to FIG. 2 of the drawings, a water heater according to asecond exemplary embodiment of the first aspect of the invention issimilar in many respects to the embodiment described with reference toFIG. 1, and like components are denoted by the same reference numerals.Thus, the water heater comprises a housing 2 of metal or shieldedpolymer material within which is housed a channel 1 having an inlet 10and an outlet 20. The channel 1 may be entirely helical as describedwith reference to the first exemplary embodiment. However, it mayalternatively be only partially helical (for example, proximate theinlet 10 and the outlet 20 only), with the remainder of the channel 1being substantially straight, as shown. In yet another embodiment, thechannel 1 may not be helical at all, but instead of wider diameter thanthe inlet 10 and outlet 20 to slow the flow of water between the two.

In this embodiment, a large proportion of the microwave power source 3is housed in a separate chamber 12 within the housing 2, with only asmall portion of the magnetron protruding through an opening of thechamber 12 into the main body of the housing 2. A cooling fan or othercooling device 4 is provided within the magnetron chamber 12, whichincludes an air inlet 5 for permitting air from outside the housing 2 toenter the magnetron chamber 12 and an air outlet 6 a for expelling airtherefrom. The cooling fan operates to draw cool air through the inlet 5into the magnetron chamber 12, across the magnetron unit to cool it andexpel the resulting warm air from the magnetron chamber 12 into the mainbody of the housing 2.

Also provided within the housing 2 is a waveguide 7 for directingmicrowave radiation generated by the magnetron 3 (and the warm airexpelled from the magnetron chamber 12 during the cooling process)towards the channel 1. A second air outlet 6 b is provided in thehousing wall for expelling air from the housing 2. In use, once again,power is supplied to the magnetron 3 which operates to produce microwaveradiation and emit said radiation into the area within the housing 2between the waveguide 7 and the magnetron chamber 12. The microwaveradiation generated by the magnetron 3 is directed by the waveguide 7towards the channel land acts to heat water which is flowingtherethrough between the inlet 10 and the outlet 20. During operation,the cooling fan 4 is operated to draw cool air into the magnetronchamber 12, across the magnetron 3 to cool it and out of the air outlet6 b into the housing 2. The expelled warm air is directed by thewaveguide 7 towards the channel 1 and provides an additional heatingsource to assist in the heating of the water therein. Thus, the water isefficiently heated as it flows through the channel 1 and no storage tankis required: the water can simply be pumped to wherever it is requiredfor use directly from the water heater.

Referring to FIG. 3 of the drawings, a water heater according to a thirdexemplary embodiment of the first aspect of the present invention isonce again similar in many respects to the embodiments described withreference to FIGS. 1 and 2, and like components are denoted by the samereference numerals. In this case, however, the conduit through whichwater to be heated flows is provided in the form of a substantiallycylindrical chamber 1 within the housing 2. A generally triangularchamber 8 is provided within the housing 2 for housing the electroniccomponents required for controlling the water heater.

Once again, a magnetron chamber 12 is provided within which themagnetron unit is substantially housed, with only a small portion of themagnetron protruding from the top of the chamber 12 into the housing.The profile of the chamber 8 and the chamber 12 in combination providesa waveguide 7 for directing microwave radiation generated by themagnetron 3 towards the cylindrical chamber 1 through which water to beheated flows. Once again, a cooling fan 4 is provided within themagnetron chamber, which draws air into the magnetron chamber 12 throughan inlet 5 and across the magnetron unit 3 to cool it. Warm air is thenexpelled from the magnetron chamber 12 through the air outlets 6 a and 6b. Warm air expelled through the outlet 6 b is directed by the waveguide7 towards the cylindrical chamber 1 to assist in the heating of thewater therethrough, and is then expelled through another air outlet 6 cin the wall of the housing 2.

In the case of all three of the above-described embodiments, operationof the magnetron 3 is triggered by the flow of water through the conduit1. The commencement of flow of water through the conduit 1 (which isachieved by, for example, somebody running a tap connected to thesystem) is detected by the electronic control circuit provided in thechamber 8, which then switches on the power supply to the magnetron 3and triggers its operation. Thus, the water is heated and supplied upondemand. When the water ceases to flow through the conduit 1, this isdetected by the control circuit, which switches off the power supply tothe magnetron 3 such that it stops operating.

It will be appreciated that the size and position of the microwave (orother radio frequency wave) source is dependent on the intendedapplication and requirements of any particular embodiment of the presentinvention; and the present invention is therefore not intended to belimited in this regard. It will also be appreciated that the chamber (orother unit) required to support or house the electronic control unit forthe apparatus may be provided in or on the apparatus itself, or it maybe provided entirely separately therefrom, according to userrequirements and environmental considerations. Further, in the casewhere a waveguide is provided to direct the radio frequency wavestowards the intended target, it will be appreciated that the size anddesign of such a waveguide will only be dependent on the design of theoverall apparatus and is limited only in terms of the aim it is requiredto fulfill within such apparatus.

Referring to the FIG. 4 of the drawings, a heating apparatus or“radiator” according to an exemplary embodiment of the second aspect ofthe present invention comprises a housing 100 of a substantiallythermally conductive material. Fluid, such as water, is introduced intothe housing 100 via a fill plug 300, provided in the upper wall of thehousing 100. When the housing 100 is filled to a predetermined levelwith water, the housing 100 is sealed for use, such that the water inthe housing 100 comprises a substantially static body of water withinthe housing 100. A heating unit 200 is provided on a side wall of thehousing 100, in communication with the interior thereof. The lower wallof the housing 100 may also be provided with a drainage plug 400 forpermitting the drainage of the water so that it can be renewed, or theapparatus can be moved.

Referring to FIG. 5 of the drawings, the heating unit 200 comprises abox-like housing containing a radio frequency heating source 500. Awaveguide 900 is provided for directing the radio frequency waves fromthe source 500 into the interior of the heating apparatus housing 100.

A cooling fan 600 is provided which draws cooling air into the heatingunit via air inlet 610, across the radio frequency heating source 500,and expels the warm air from the heating unit via air outlet 700.Control electronics 800 are provided for controlling the operation ofthe radio frequency heating source, according to heating requirementsselected by a user.

Referring to FIGS. 6A and 6B of the drawings, it can be seen that theheating unit 200 may be provided externally on the outside of thehousing 100 (FIG. 6A). Alternatively, it may be provided inside thehousing 100 (FIG. 6B).

The provision of one or more aerials in the flow or body of water wouldenhance the performance of all of the above-described systems. Theaerial(s) may comprise metal rod(s), pipe(s), tube(s), wire(s), piece(s)of metal or wire wool and/or metal filings, although the choice ofaerial will depend on several different factors.

At least three things happen when microwaves encounter a load: Theenergy can be reflected, transmitted, or absorbed depending on itsproperties. A load placed in a microwave cavity may therefore not heatat all, may heat quickly, may heat after a certain time (slow process),and/or generate hot spots. It is thus important to know beforehand thematerial properties as they determine the materials interaction withmicrowaves, ie whether it is opaque, transparent or Lossy.

Any homogeneous, isotropic, and linear dielectric material ischaracterised by a frequency—dependent absolute complex permittivity,known as the relative dielectric constant (e″). This is used as arelative measure of the microwave energy density in the material. Theimaginary part e″″, known as the relative loss factor, accounts for allthe internal loss mechanisms. It indicates how well a material absorbsenergy from the electric field passing through it and how much energy isconverted to heat. A lossy material with a high e″″ will thereforeabsorb energy well and heat quickly, provided that it has a small sizewith respect to the penetration depth. On the other hand, if thematerial has a very low e″″ the material becomes transparent. Therefore,materials with middle range values of e″″ (i.e. e″″<3) are suitable fordielectric heating, e can be used to indicate how much energy isreflected away from a material and how much is transmitted.

Taking these factors into consideration, experiments were set-up in thefollowing order, 300 ml of tap water in a Pyrex beaker was placed in thecentre of a domestic microwave oven, and set to full power (900 watts).Water reached 100 °° C. after 180 seconds. Apparatus was allowed to cooland again the beaker was filled to 300 ml mark. Two stainless steel rodseach measuring 3 mm diameter and 150 mm in length were placed into thebeaker and diagonally crossing and touching in the water with approx. ⅓of its length protruding out of the beaker, again full power wasapplied. After approx. 30 seconds bubbles were forming around thediagonally crossed stainless steel rods submerged in water and reached100°° C. after 120 seconds. Therefore, suggesting the rods were actingas antennas concentrating the energy, allowing the water to heatquicker.

Valuation

Water measured in kilos is 0.1 kg=100 ml.

Specific heat capacity of water=4.2×10³J/Kg⁻¹/K⁻¹Q =mc(θ?₂−θ?₁)

This expression is useful in heat calculations and gives the quantity ofheat (Q) taken in by a body of mass (m) and mean specific heat capacity(c) when its temperature rises from θ?₁ to θ?₂ it also gives the heatlost by the body when its temperature falls from θ?₂ to θ?₁.

In words, we can say:

Heat Given Out=Mass×Specific Heat Capacity×Temperature Change (or TakenAway)

Therefore, if a measured amount of water is taken to be m=0.3 kg and theapproximate specific heat capacity of water at room temperature is4.2×10³J/Kg⁻¹/K⁻¹ and θ?₁=15°° C. Heating that amount of water for agiven time of 180 seconds gives θ?₂ to be 100°° C. giving D_(T)=85°° C.

We can say:Q=mc D _(T)Q=0.3×(4.2×10³)×85Q=107,100J

Delivered energy (Power) from microwave if:1 watt=1J/second.

Therefore, a 900 watt microwave delivers 900 J/second.In 180 seconds=900×180=162,000J(Total)

Target absorbed=107,100J of produced J. Therefore, absorbing 66.1%

Heating water with a submerged stainless steel rod for a given time of120 seconds, gives θ?₂ to be 100°° C. giving D_(T)=85°° C.

We can then say:Q=mc D_(T)Q=0.3×(4.2×10³)×85Q=107.100J

Delivered energy (Power) from microwave if:1 watt=1J/second.

Therefore, a 900 watt microwave delivers 900J/second.In 120 seconds=900×120=108,000J (Total)

Target absorbed=107,100J of produced J. Therefore, absorbing 99.2%

Referring to FIG. 7 of the drawings, an exemplary embodiment of thethird aspect of the present invention comprises a rectangular waveguide700 providing a heating cavity having two adjustable end plates 701,702, such that the length of the waveguide 700 can be adjusted, asrequired, using screw members 703, 704. In this exemplary embodiment ofthe invention, the heating cavity comprises a single mode waveguide 700having a single heating location through which a pipe or channel 705passes. Thus fluid to be heated flows in the pipe through the waveguide700 and passes through the heating location or “hot spot”. The systemmay be an open-loop system in which water from a supply is heated as itpasses through the heating cavity and then dispensed for use asrequired. Alternatively, it may be a closed-loop system in which thesame body of fluid flows around in a loop, is heated within the heatingcavity as it passes through and then passes through some form of heatexchanger (where it is cooled), before flowing back into the heatingcavity.

The single mode waveguide 700 providing the heating cavity is achievedby tuning the end plates 701,702 to exactly one quarter wavelength (ofthe radiation source waveform) such that the radiation transmitted fromthe radiation source (in this case, magnetron 706) to the heatinglocation is exactly one waveform 707, as shown. Any error in tuning thewaveguide would result in the radiation source within the waveguideincluding or comprising a partial waveform, which would cause reflectionof the source wave within the waveguide, thereby attenuating theradiation source wave and reducing the efficiency of the system.

Within the pipe or channel, there is provided one or more aerials 708.The or each aerial may comprise a metal rod, tube, wire or pipe, forexample, and/or metal pieces or filings, but is in any event preferably(but not necessarily) a solid member (as opposed to reticulated such asmesh or wire wool). The aerial(s) may comprise an insulative coresurrounded by a conductive material (for example, metal wire coiledaround a carbon rod), but the invention would work equally well using anaerial comprising a metal member completely or partially covered in aninsulative material, such as a plastic sheath or the like. This isbecause the aerial operates to concentrate the radiation source at theheating location, rather than absorbing the radiation so that it heatsup and transfers heat to the fluid, as in some prior art arrangements.

It may be desirable, under some circumstances, to delay the flow offluid through the heating cavity so that the fluid is in there longenough to be heated sufficiently. As stated above, this can be achievedby providing, for example, a helical pipe section within the cavity.Alternatively, some means for delaying fluid flow may be used. Forexample, an electronic sensor may be employed to monitor the temperatureof fluid at the outlet, and cause a control system to adjust the fluidflow rate accordingly; or a mechanical cam may be used which can berotated to selectively decrease the diameter of the pipe 705 inside oroutside the heating cavity so as to reduce the fluid flow.

As stated above, a cooling fan (not shown) or similar means may beprovided to draw cooling gas over the magnetron 708 so as to cool it,although it is envisaged in another embodiment of the invention, forpipe 705 to be wrapped around the magnetron 706 within the heatingcavity, such that heat generated by the magnetron passes directlythrough the pipe to the fluid. A cooling fan may then also be providedto improve cooling efficiency (although this would not be essential inall cases).

The structure of a heating cavity according to an exemplary embodimentof the invention can be seen in more detail in FIGS. 8 to 10 of thedrawings.

In an alternative embodiment, the heating cavity may instead comprise amulti-mode waveguide, such that there are a plurality of heatinglocations or “hot-spots” therein. The system may then be arranged to“train” the flow of fluid through each heating location and, possibly,reduce the fluid flow at one or more of those heating locations to allowthe fluid thereat to be sufficiently heated.

It will be appreciated that a magnetron generally has a predetermined,somewhat limited, life. Thus, one embodiment of the invention maycomprise a plurality of (preferably) single mode waveguides, each havinga magnetron, and through each of which the fluid is arranged to flow. Acontrol system is provided which causes a single heating cavity to beoperated at any time (i.e. only one magnetron is energised at a time).The control system may, for example, be arranged to switch each heatingcavity in turn, or switch one heating cavity on when another fails.

In general, embodiments of the present invention have been describedabove by way of examples only with reference to the accompanyingdrawings, and it will be apparent to a person skilled in the art thatmodifications and variations can be made to the described embodimentswithout departing from the scope of the invention as defined in theappended claims.

1. Fluid heating apparatus comprising a heating cavity and one or moreradio frequency wave heating sources arranged to emit electromagneticradiation into said heating cavity such that a body of fluid disposedtherein or fluid flowing or passing therethrough is heated, theapparatus further comprising one or more aerials disposed within thebody or flow of fluid to be heated, the or each aerial comprising amember arranged to transmit or receive electromagnetic waves.
 2. Heatingapparatus according to claim 1, wherein said fluid is a liquid (e.g.water).
 3. Heating apparatus according to claim 1, wherein said heatingsource is electromagnetic radiation in the range between 3KH_(z) and 300GH_(z), more preferably 100 MH_(z) and 100 GH_(z), yet more preferably100 MH_(z) and 10 GH_(z), and yet more preferably 300 MH_(z) and 3GH_(z), for example, a microwave heating source.
 4. Heating apparatusaccording to claim 1, wherein said aerial or aerials is/are at leastpartially metal member(s).
 5. Heating apparatus according to claim 4,wherein said metal member(s) comprise one or more solid members, such asa rod, tube, pipe, wire, metal pieces or filings.
 6. Heating apparatusaccording to claim 1, wherein said aerial or aeriels each comprise aninsulative member and at least one radiation absorption means affixed toor at least partially surrounding said insulative member.
 7. Heatingapparatus according to claim 1, wherein the or each aerial comprises ametal member at least partially surrounded or covered with an insulativematerial.
 8. A method of heating fluid, comprising the steps ofproviding a heating cavity within which is disposed a body of fluid tobe heated or through which fluid to be heated is caused to pass or flow,emitting radio frequency wave radiation into said heating cavity suchthat said fluid is heated thereby, and providing one or more aerialswithin said body or flow of fluid, the or each aerial comprising amember arranged to transmit or receive electromagnetic waves.
 9. Amethod according to claim 8, wherein said fluid is a liquid (e.g.water).
 10. Fluid heating apparatus comprising a heating cavity and asubstantially fluid-tight pipe or channel within said heating cavity,the pipe or channel having an inlet and an outlet, means for causingfluid to flow or pass through said pipe or channel from said inlet tosaid outlet, and one or more radio frequency wave heating sourcesarranged to emit electromagnetic radiation into said heating cavity suchthat fluid is heated thereby as it flows or passes through said pipe orchannel from said inlet to said outlet.
 11. Heating apparatus accordingto claim 10, wherein said fluid is a liquid (e.g. water).
 12. Heatingapparatus according to claim 10, wherein said pipe or channel comprisesa conduit of metal, plastic or any other suitable material.
 13. Heatingapparatus according to claim 10, further comprising one or more aerialsdisposed within the flow of fluid to be heated, the or each aerialcomprising a member arranged to transmit or receive electromagneticwaves.
 14. Heating apparatus according to claim 13, wherein said one ormore aerials at least partially comprise one or more metal members. 15.Heating apparatus according to claim 13, wherein said one or moreaerials at least partially comprise carbon, or other suitablenon-metallic material.
 16. Heating apparatus according to claim 14,wherein said one or more metal members comprise, or include one or moresolid members, such as a rod, tube, pipe, wire, metal pieces or filings.17. Heating apparatus according to claim 10, wherein said heating sourceis electromagnetic radiation in the range between 3 KH_(z) and 300GH_(z), more preferably 100 MH_(z) and 100 GH_(z), yet more preferably100 MH_(z) and 10 GH_(z), and yet more preferably 300 MH_(z) and 3GH_(z), for example, a microwave heating source.
 18. Apparatus accordingto claim 10, arranged to heat fluid to a variety of different(preferably selectable) temperatures.
 19. Apparatus according to claim18, arranged to heat fluid to a temperature in a range between 20° C. to500° C.
 20. Apparatus according to claim 10, arranged to sterilizefluid.
 21. Apparatus according to claim 10, comprising control means forcontrolling variables of the apparatus, when in use, to produce adesired fluid temperature at the outlet.
 22. Apparatus according toclaim 10, wherein said fluid flows from a fluid supply means and isdispensed via means connected to, or in communication with said outlet.23. Apparatus according to claim 10, comprising a closed loop system inwhich the same body of fluid flows into and out of said heating cavity,passes through a heat exchange means and then flows or passes back intosaid heating cavity via said inlet.
 24. Apparatus according to claim 21,comprising sensor means for sensing the rate of flow of fluid intoand/or through said pipe or channel, the control means being arranged tocontrol the frequency of said one or more heating sources and/or saidrate of flow of fluid so as to produce a desired fluid temperature atthe outlet.
 25. Apparatus according to claim 21, comprising a mechanicalcam means for regulating the flow of fluid through said pipe or channelby selectively varying the diameter thereof.
 26. Apparatus according toclaim 21, comprising sensor means for sensing the fluid temperature atthe outlet, the control means being arranged to control the frequency ofsaid one or more heating sources and/or the rate of flow of fluid intoand/or through said conduit so as to produce a desired fluid temperatureat the outlet.
 27. Apparatus according to claim 20, comprising anairtight storage tank for storing fluid sterilized by said apparatusuntil it is required for use.
 28. Apparatus according to claim 10,wherein said channel or pipe comprises a helical or otherwise shapedtube or channel, or network of channels or tubes for reducing the flowrate of fluid through said channel or pipe from that at which it enterssaid channel or pipe.
 29. Apparatus according to claim 10, comprisingone or more channels or pipes.
 30. Apparatus according to claim 10,wherein said one or more channels or pipes are formed of thermallyconductive material.
 31. Apparatus according to claim 10, comprising oneor more waveguides to aid in the transmission and direction of the radiofrequency waves emitted by the heating source towards the conduitthrough which the fluid to be heated is passing or flowing. 32.Apparatus according to claim 31, wherein said heating cavity comprisesor includes a single mode waveguide.
 33. Apparatus according to claim31, wherein said heating cavity comprises or includes a multiple modewaveguide including a plurality of heating locations.
 34. Apparatusaccording to claim 33, comprising means for slowing or delaying the flowof fluid through said heating cavity at one or more of said heatinglocations.
 35. Apparatus according to claim 32, including means forstopping and holding a body of fluid at the or each heating locationsuch that a fixed body of fluid is heated.
 36. Apparatus according toclaim 10, comprising a plurality of heating cavities, and means forreflectively switching between said heating cavities.
 37. Apparatusaccording to claim 10, wherein commencement of flow of fluid triggersthe operation of the radio frequency wave heating source.
 38. Apparatusaccording to claim 10, comprising cooling means for cooling said heatingsource in operation.
 39. Apparatus according to claim 10, wherein saidchannel or pipe is disposed adjacent said heating source, such that heatgenerated by said source is transferred to the fluid within or flowingor passing through said channel or pipe.
 40. Apparatus according toclaim 38, wherein said cooling means comprises a cooling fan for drawingcooling air across said heating source in operation.
 41. Apparatusaccording to claim 40, wherein said air, once it has been drawn acrosssaid heating source, is used to aid in heating said fluid flowing orpassing through said conduit.
 42. Apparatus according to claim 10,wherein said apparatus is portable.
 43. A method of heating fluidcomprising the steps of providing a heating cavity and a substantiallyfluid-tight pipe or channel within said heating cavity, the pipe orchannel having an inlet and an outlet, causing fluid to flow or passthrough said pipe or channel from said inlet to said outlet, applyingradio frequency wave radiation into said heating cavity around said pipeor channel such that fluid is heated thereby as it flows through saidpipe or channel from said inlet to said outlet.
 44. A method accordingto claim 43, wherein said fluid comprises a liquid (e.g. water).
 45. Amethod according to claim 43, including the step of delaying the flow offluid at one or more selected locations within said heating cavity whereit is heated by said radio frequency wave radiation.
 46. (canceled) 47.Heating apparatus for emitting heat into the surrounding atmosphere,said apparatus comprising a thermally conductive housing containing abody of fluid therein, when in use, and one or more radio frequencyheating sources for heating said body of fluid in said housing, heatfrom said body of fluid being conducted to said housing and from saidhousing into the surrounding atmosphere.
 48. Heating apparatus accordingto claim 47, wherein said fluid is a fluid, and more preferably water ora water-based fluid.
 49. Heating apparatus according to claim 47,further comprising one or more aerials disposed in said body of fluid.50. Heating apparatus according to claim 49, wherein said one or moreaerials is/are or include metal member(s), and more preferablysubstantially solid metal members such as metal rods, pipes, tubes orwires, pieces of filings.
 51. Heating apparatus according to claim 47,wherein said one or more radio frequency heat sources are supplied withelectrical power from a mains supply, generator, and/or a batterysupply.
 52. Heating apparatus according to claim 47, comprising acontrol unit, which is preferably wireless, for controlling theoperation thereof.
 53. Heating apparatus according to claim 47,comprising a drainage plug for allowing said fluid to be drained out ofsaid housing.
 54. Heating apparatus according to claim 47, comprising afill plug for introducing fluid into said housing.
 55. Heating apparatusaccording to claim 47, including an expansion tank or similar vessel.56. Heating apparatus according to claim 47, comprising means forcooling said one or more radio frequency heat sources, and/or means forventing warm air, and/or waveguide means for transferring to radiofrequency waves into the fluid chamber defined by the internal confinesof the housing causing the fluid therein to be heated.
 57. Heatingapparatus according to claim 47, comprising means for agitating thefluid within the housing, or causing it to circulate therein. 58.Heating apparatus according to claim 57, comprising a waveguide andradio frequency heating source, and means for causing the fluid tocirculate within the housing, through said waveguide.
 59. (canceled)